1. Field of the Invention
The present invention relates to a deposition donor substrate used for deposition of a material that can be deposited by an evaporation method and a method for manufacturing a light-emitting device using the deposition donor substrate.
2. Description of the Related Art
Light-emitting elements, which use organic compounds as a light emitter and are characterized by the thinness, lightweight, fast response, and direct current low voltage driving, are expected to be applied to next-generation flat panel displays. In particular, display devices having light-emitting elements arranged in matrix are thought to be superior to conventional liquid crystal display devices for their wide viewing angles and excellent visibility.
As for a light-emitting mechanism of a light-emitting element, an EL layer is interposed between a pair of electrodes and voltage is applied, whereby electrons injected from a cathode and holes injected from an anode recombine in an emission center of the EL layer to form molecular excitons, and the molecular excitons release energy when relaxing into a ground state; therefore, light is emitted. A singlet excited state and a triplet excited state are known as excited states, and it is thought that light emission can be obtained through either of the excited states.
An EL layer included in a light-emitting element includes at least a light-emitting layer. In addition, the EL layer can have a stack structure including a hole-inject layer, a hole-transport layer, an electron-transport layer, an electron-inject layer, and the like, in addition to the light-emitting layer.
In addition, EL materials for forming EL layers are broadly classified into low molecular (monomer) materials and high molecular (polymer) materials. In general, a film of a low molecular material is often formed by an evaporation method, and a film of a high molecular material is often formed by an inkjet method or the like.
An evaporation apparatus which is used in an evaporation method has a substrate holder on which a substrate is set; a crucible (or an evaporation boat) containing an EL material, i.e., an EL layer-forming material; a heater for heating the EL material in the crucible; and a shutter for preventing the EL material from being diffused during sublimation. The EL material heated by the heater is sublimed and deposited to the substrate.
In order to form a uniform film, actually, a deposition target substrate needs to be rotated, or the substrate and the crucible need to be separated from each other by at least a certain distance. In addition, when films of different colors are separately formed using plural kinds of EL materials through a mask such as a metal mask, it is necessary that the distance between pixels be designed to be large and that the width of a partition layer (bank) formed using an insulator between pixels be large. Such needs are major problems in advancing high definition (increasing the number of pixels) and miniaturization of display pixel pitches along, in a light-emitting device including a light-emitting element. Further, there is a problem in that, with a larger deposition target substrate, a mask covering a substrate sags and accordingly an EL layer cannot be formed accurately.
Further, as for flat panel displays, it has been necessary to solve those problems as well as to improve productivity and reduce costs, in order to achieve higher definition.
Thus, a method for forming an EL layer of a light-emitting element through laser thermal transfer has been proposed (e.g., see Patent Document 1). Patent Document 1 discloses a transfer substrate which has a photothermal conversion layer including a low-reflective layer and a high-reflective layer, and a transfer layer, on a supporting substrate. Irradiation of such a transfer substrate with laser light allows the transfer layer to be transferred to an element-forming substrate.                [Patent Document 1] Japanese Published Patent Application No. 2006-309995        